17m doesn't know how to approach 17f (Is a pussy)

Hi! I've kinda had a crush on this one particular girl at my school for more or the less 3 years. I asked her out once like 2 years ago, but she said she didn't have time and I kinda had lost interest there for a moment.

(Kinda made me depressed a bit the last months)

Now I've finally found motivation to try to ask her out, but she's always with her friends when I see her (and I need to be together in the same classes etc. with all those people for at least another year of school). I'm kind of a pussy to not just walk up to her and ask her.

Now I'm thinking to ask her via a Message, but I actually had planned to avoid it. What are you people thoughts on just asking her via a snapchat/whatsapp message?